From U.S. Pat. No. 3,016,860 a sail boat is known, which has at the uppermost portion of the main sail an inflatable air bag which is inflated automatically like a balloon, when the boat capsizes. However, this air bag will produce a large air resistance when inflated and therefore cannot be used during normal sailing.
From Swiss patent specification No. 603 392 a windsurfer is known, by which the sail is provided with a buoyancy body consisting of a bag containing buoyancy material and being adapted to be folded around the uppermost portion of the mast and buttoned on to the sail, e.g. by means of press fasteners. A device of this kind cannot be used by sailing dinghies and keel boats, the sails of which are hoisted and lowered by means of a halyard. In addition, the mast, the buoyancy body and the sail form together a clumsy profile having a large "drag" and a small "lift".